This invention relates to an apparatus for removing airborne particulate, including dust, from an airstrean.
This invention has particular application in cleaning the contaminated air being drawn from gritblasting operations in preparation of thermal coating in a coal fired boiler. The invention may also be applied to provide air cleaning for grit blasting operations in preparation for spray painting and to remove paint particulate from the contaminated airstream. The invention may also be used for cleaning the air from such operations in vessels aid structural steel as defined below.
The term boiler is used herein to include, without limiting, boilers fired with diesel or wood waste and chemical recovery boilers. The term vessel is used herein, without limiting, to include storage tanks, continuous or batch digesters, refining columns and the hulls or interiors of ships. The term structural steel is used herein to include, without limiting, supporting steel for boilers, supporting steel for vessels, bridges, and control gates for dams.
In the past, cleaning of contaminated air in such applications has been achieved by large electric driven or engine driven fans drawing the air through cyclones, a series of filters, or a combination of both. These xe2x80x9cdust collectorsxe2x80x9d as they are referred to in the industry are large and heavy and usually mounted on large trucks or flatbed trailers and quite often cannot be located adjacent to the worksite, thus requiring the use of long lengths of pipe or flexible ducting to transport the contaminated air, They may have self-cleaning filters or bags. Over time the filters or bags have to be replaced.
Accordingly, it is an object of the present invention to at least partially overcome the disadvantages of the prior art by providing apparatus for particulate removal adjacent to one or more selected work sites and to provide for sizing the apparatus to correspond to the scope of work being performed.
To this end, in one of its aspects, the invention provides the ability to locate the apparatus adjacent to a selected worksite. This is facilitated by the apparatus being relatively lightweight, portable, modular and consequently, its ability to be relative quickly assembled at the worksite. The components may be adapted for transport in a freight or personnel elevator such as commonly employed in industrial plants. The apparatus can also be sized to accommodate a small worksite or plurality of worksites.
The apparatus includes in one embodiment, elements constructed of panels of plastic grid and mesh held together in a xe2x80x9cCxe2x80x9d channel around the perimeter of the panels. Water manifolds having substantially the same outer dimensions as the elements are provided for mounting upstream of each element. The manifolds have orifices pointing generally inwards in the plane of the manifold frame. The water manifold is hollow so as to form a manifold supplying water to the orifices. The orifices are sized to create a mist or spray.
A plurality of elements and manifolds are mounted in at least one chamber, so as to extend laterally from each side and from top to bottom of the chamber thus preventing airflow bypassing around the elements. The contaminated airstream is thereby forced or drawn through the chamber through the elements and manifolds. The chamber or a plurality of interconnected chambers may be mounted on, so as to be supported by, a system scaffold, such as the Layher-type scaffold. In each chamber, as the particulate laden airstream passes through the manifold, water droplets in the mist or spray from the manifold may adhere to the airborne particulate and then either fall into a collection hopper, or otherwise be mixed into, so as to mingle with and be carried by the airstream. As the mist in the airstream passes through the corresponding element some or many of the particulate laden water droplets contact and adhere to the surfaces of the array of grids or mesh in the elements. The water droplets coalesce on the surfaces of the grids or mesh until blown or drawn by gravity from the grids or mesh so as to fall into the hopper. In this manner particulate are removed from the airstream,
Solid panels form sides, ends and top of each chamber. The floor of each chamber may be formed as a collection hopper or funnel or catch-trough or the like for collecting the slurry of water and particulate. In one embodiment, the hopper directs the slurry to a drain. A drain line may take the slurry from the drain to a settling tank. Tie tank may leave a plurality of weirs to promote settling out of the sediment. A submersible pump may be located in the downstream-most settling compartment to pump the water back into the manifolds so as to recirculate and reuse the water. This is useful, as the system is intended to be temporary and as it lends to the portability of the system so as to operate more unintrusively in a plant and eliminates the need to dump large quantities of water or slurry,
The power source may be a pneumatic, i.e. air powered, air mover such as an air reaction fan, or other in-line air moving or other air motivating means, which is relatively compact, lightweight and capable of moving relatively large volumes of air. Air reaction fans are well adapted because they may be shock-proof in wet conditions and safe in volatile atmospheres when properly grounded.
The contaminated air is drawn into the chambers through an inlet on the upstream end of the first, i.e. upstream, chamber. The airstream then passes through a plurality of elements in each chamber, although a plurality of chambers may not be required depending on the demands of the specific application, Each element is mounted in the chamber so as to seat across the chamber to prevent airflow bypassing the element. Otherwise it has been found that an airflow bypass reduces the efficiency of slurry extraction. Each element has a corresponding water sprayer such as a perforated manifold mounted adjacent or to the upstream side of the element. A space is provided between elements for example when the elements are mounted at either end of a chamber at the edges of the hopper. Adjacent chambers are connected by, for example, a short duet. The second or additional chambers may have the same dimensions as the first chamber and contain the same plurality and arrangement of elements and corresponding water sprayers or manifolds. The air mover as described above may be mounted at the downstream end of the second or downstream-most chamber. The air mover may be mounted on the end panel or on the roof of the downstream chamber to suit the particular application. A smooth duct mounted to the air mover carries the moisture laden air to a remote exhaust location where it will not affect other worksites.
In the upstream chamber, the upstream element or element and manifold pair may be inclined downstream so as to leave the root or base of the clement against the edge of the hopper, thereby providing an airspace or gap between the inlet and that element. This allows the airstream to better mix and more uniformly spread out into the chamber before impinging the first or upstream grids or mesh in the upstream element. This spreading introduces a more uniform flow rate across the face of the element and a more uniform flow rate through the entire area of the element to optimize the efficiency of coalescing of the slurry on the grid or mesh members. Inclining the element also increases the apparent surface area of the grids or mesh as the airflow impinges the grids or mesh at an angle. The downstream-most clement may be inclined upstream from a base edge in contact with the downstream edge of the corresponding hopper.
In summary a device for removing airborne particulate of the present invention includes at least one chamber having an airstream inlet at an upstream end and an airstream outlet at a downstream end, an air mover cooperating with the at least one chamber so as to urge an airborne particulate laden airstream into the at least one chamber through the inlet, along a flow path through the at least one chamber, and out of the at least one chamber through the outlet, at least one water sprayer mounted to the at least one chamber for mixing a spray of water with the airstream in the flow path, at least one slurry collecting element mounted entirely across and in the flow path so as to seal across the chamber to prevent bypass of the airstream around the collecting element, the collecting element downstream of the water sprayer, the at least one slurry collecting element including at least one array of slurry collecting members mounted so as to pass at least a portion of the airstream through the array, the at least one chamber having a slurry remover therein for removing from the at least one chamber slurry collected by the at least one slurry collecting element.
The, at least one, array may be a lattice including at least one grid.
The, at least one, rigid grid may be at least two parallel adjacent rigid grids. An upstream-most collecting element may be inclined relative to the airstream.
The, at least two, parallel adjacent rigid grids may be offset relative to one another so as to reduce in size an effective grid spacing in the flow path. The offset may be substantially one-half of a grid spacing of one of the at least two parallel adjacent rigid grids.
The water may be recirculated from the slurry remover to the at least one water sprayer.
The lattice may further include a mesh mounted parallel to the at least one rigid grid.
The water sprayer may include a water manifold extending at least partially around the at least one chamber. The water manifold may be a water conduit mounted around an interior perimeter, substantially lateral cross-section of the at least one chamber, the conduit having orifices in spaced array therearound directed into the flow path. The manifold may be mounted within the at least one chamber. The manifold may be mounted adjacent and parallel to the at least one lattice of slurry collecting members.
The inlet may be an airstream diffuser so as to slow the airstream upstream of the at least one water sprayer. The, at least one, water sprayer may be spaced apart from the inlet so as to allow the airstream to slow m the at least one chamber upstream of the at least one water sprayer.